It is previously known in this art to permanently anchor all prostheses in the maxillary by means of helicoid anchorage elements, so-called fixtures, of a bio-compatible material, preferably pure titanium. The method which has displayed the highest degree of anchorage stability and which has successfully been used clinically for more than 20 years is the so-called osseointegration method developed by professor Per-Ingvar Branemark et al and described in, for example,
Branemark/Zarb/Albrektsson: "Tissue-Integrated Prostheses", Quintessence Books, 1985.
The method is based on a highly exact and atraumatic implant technique of the fixture such that a direct contact--in other words an exact adaptation without interjacent soft tissue--occurs between the fixture and the bone tissue. Such a direct contact between fixture and bone tissue provides the best preconditions for a really permanent fixation of, for example, a dental prosthesis.
The helicoid fixtures of pure titanium are operated into the maxillary in a first surgical operation which is followed by an unloaded healing phase of critical length during which time the fixture is covered by intact mucous membrane. During this healing phase, the bone tissue grows onto and forms a unit with the implanted fixture. In a second operation, the fixture is then exposed and a substantially tubular spacer is applied to the fixture by means of a spacer screw. Subsequently, the dental prosthesis proper--in the form of a bridge construction--is united to the fixture by means of a fixing screw which, in its turn, anchors in the spacer screw.
A bridge construction is anchored in place by means of a plurality of fixtures, for example six in number, and corresponding spacers which constitute connection elements between the bridge construction and the fixtures. To be able to absorb the extreme oral loadings to which the screw connection is subjected, the spacers are of a bio-compatible material of extremely good strength properties, for example titanium or the like.
Normally, the connection portion (base portion) of the spacer against the fixture will, after the operation, be enclosed by the gingiva. However, the major portion of the spacer will project up above the edge of the gingiva in that gap which is formed between the gingival edge and the joint surface of the bridge construction. Normally, such exposure of the spacer will seldom constitute an inconvenience, since the spacer is concealed behind the patient's lips. However, in certain cases when the lips are raised considerably, the spacers will also become visible during speech and normal mimicry, a factor which may be disconcerting for esthetic reasons, because of the visible contrast of the metal surface of the spacers against the surrounding dental cervix and gingival colour of the patient.
Even in those cases where such spaces are very seldom exposed to view, it may be psychologically disturbing for the patient. Nor is it possible to design the bridge construction in such a manner that it descends to the gingival edge and masks the spacers, since there must be a sufficiently wide gap or space between the gingival edge and the joint surface of the bridge construction about the spacer in order to make possible cleaning the interface zone between the implant material and the gingival tissue. Such cleaning is of vital importance to prevent occurrence of gingivitis, which may spread in the interface zone between the implant material and the bone tissue and jeopardize the anchorage of the dental implant.